1. Field of the Invention
This invention relates to a disc cartridge housing therein a disc on which desired information signals are recorded, such as an optical disc or a magneto-optical disc, and, above all, a disc which may be clamped to a disc rotating and driving unit by taking advantage of the force of magnetic attraction.
2. Description of the Prior Art
There has hitherto been proposed a disc for recording desired information signals, such as an optical disc or a magneto-optical disc.
The disc of this type of an extremely small size capable of recording information signals with high density is proposed. For example, in the case of a magneto-optical disc, a disc having a diameter of not more than 64 mm, is proposed.
The magneto-optical disc which is small-sized and capable of high density recording is loaded on the disc rotating and driving unit and rotated at a higher velocity. As the disc is rotated at the higher velocity, a light beam from an optical pickup is irradiated on one or more fine recording tracks formed on a major disc surface, while an external magnetic field is applied by a magnetic head, to record desired information signals on the disc.
For accurately irradiating the light beam on the fine recording track during the high velocity disc rotation, it is necessary for the magneto-optical disc to be positively secured to a disc table of the disc rotating and driving device and to be loaded thereon with the center of rotation of the disc correctly aligned with the axis of the disc table.
For positively loading and securing the small-sized magneto-optical disc on the disc table with high accuracy, there is proposed a disc loading system in which a metallic plate formed of a magnetic metal material is arranged on the magneto-optical disc and attracted by a magnet provided on the disc table for clamping the disc to the disc table.
A magneto-optical disc 1 shown in FIGS. 1 and 2 is proposed as a magneto-optical disc employed in such disc clamping system which makes use of the magnetic force of attraction. The magneto-optical disc 1, shown in FIGS. 1 and 2, is provided with a disc substrate 2 formed as a transparent polycarbonate resin. A signal recording layer for recording desired information signals is deposited on one major surface 2a of the disc substrate 2. The opposite major surface 2b of the disc is a write/read surface. It is from the side of this write/read surface that the light beam is radiated from an optical head to the signal recording layer for recording or reproducing information signals.
Referring to FIGS. 1 and 2, a centering hole 3, engaged by a centering member arranged on the disc table of the disc rotating and driving unit, is formed at the center of the disc substrate 2. A recess 5 for housing a metallic plate 4, which is a magnetic member attracted by a magnet provided on the disc table, is formed at the center of the major surface 2a of the disc substrate 2. The recess 5 has a depth significantly larger than the thickness of the metallic plate 4. The metallic plate 4, housed within the recess 5, is formed with a downturned peripheral part 4a and a resting part 4b which is contiguous to the peripheral part 4a and rests on a resting surface 5a on the bottom of the recess 5. That is, the metallic plate 4 is formed as a cap having a height corresponding to the vertical height on the downturned part 4a and having the flange-shaped resting part 4b continuous to the downturned part 4b.
The above-described metallic plate 4 is housed within the recess 5 with the resting part 4b resting on the resting surface 5a so that a gap is defined between the outer surface of the bent part 4a and the inner surface of the recess 5. The metallic plate 4 is supported in the recess 5 by having the resting part 4b supported by a plurality of, e.g. four supporting projections 5b formed by locally thermally deforming the rim of the recess 5.
Meanwhile, an annular step 6 is formed at the center of the major surface 2b of the disc substrate 2 for surrounding the center hole 3, as shown in FIG. 2. The function of the annular step 6 is to increase the depth relative to the centering hole 3 of a centering member provided on the disc table on which the magneto-optical disc is loaded to assure positive centering of the disc 1 with respect to the disc table.
The metallic plate provided on the magneto-optical disc employed in the disc loading system which makes use of the magnetic force of attraction is attached to the major surface of the magneto-optical disc, such as with an adhesive, for closing the centering hole bored at the center of the magneto-optical disc. When the magneto-optical disc, having the metallic plate attached thereto, is set on the disc table, it is clamped to the disc table, under the force of attraction by the magnet provided thereon for rotation in unison with the disc table.
The magneto-optical disc, capable of high-density recording of information signals, is housed in a cartridge main body, as a disc cartridge, to prevent deterioration of recording/reproducing properties due to deposition of dust and dirt or damage, and is loaded on the recording/reproducing apparatus or laid in store in this state.
FIG. 3 shows an arrangement of the disc cartridge.
Referring to FIG. 3, the disc cartridge includes a rectangular cartridge main body 9 formed by abutting and connecting an upper half 7 and a lower half 8 to each other for housing the magneto-optical disc 1 therein. A disc housing section is provided in the cartridge main body 9 for rotatably housing the magneto-optical disc 1.
The cartridge main body 9 is formed with an inlet opening 10 into which the disc table of the disc rotating and driving unit rotationally driving the cartridge main body 9 is introduced when the disc cartridge is loaded on the recording/reproducing apparatus. Referring to FIG. 5, the inlet opening 10 is a circular opening formed at the mid part of the lower half 7 for exposing the inner peripheral region inclusive of the centering hole 3 of the magneto-optical disc housed within the cartridge main body 9 set on the disc table.
The upper and lower surfaces of the cartridge main body 9, that is the upper and lower halves 7 and 8, are formed with recording/reproducing apertures 11, 12 for exposing at least a part of the signal recording region of the magneto-optical disc 1 accommodated in the cartridge main body 9 to the outside across the inner and the outer peripheries of the disc. Referring to FIG. 3, the recording/reproducing apertures 11 and 12 are formed as rectangular apertures at a transversely mid part of the cartridge main body 9 extending from a position close to the inlet opening 10 towards the front side of the cartridge main body 9.
A shutter member 13 is provided on the cartridge main body 9 for closing the recording/reproducing apertures 11, 12 to prevent dust and dirt from entering by means of the apertures 11, 12 into the inside of the cartridge main body 9 and depositing on the magneto-optical disc 1. The shutter member 13 is formed by punching and bending a thin metallic plate into a rectangular frame having a U-shaped cross-section and is composed of shutter sections 13a, 13b closing the recording/reproducing apertures 11 and 12 and a connecting web 13c interconnecting the distal parts of the shutter sections 13a, 13b. A slide guide 13d is formed at one side of the connecting web 13c for guiding the shutter member 13 parallel to the front side of the cartridge main body 9.
The shutter member 13 is fitted on the front side of the cartridge main body 9 so that the shutter sections 13a, 13b are extended over the recording/reproducing apertures 11, 12. The shutter member 13 is mounted on the cartridge main body 9 for sliding between a position of closing the recording/reproducing apertures 11, 12 as shown by solid line in FIGS. 4 and 5 and a position of opening the recording/reproducing apertures as shown by broken lines in FIG. 4.
Referring to FIGS. 3 and 4, a shutter locking member 14 is provided at a corner on the front side of the lower half 7 of the cartridge main body 9 for being engaged with an engaging part 13e formed by partially bending the slide guide 13d for maintaining the shutter member 13 at a closure position for thereby preventing inadvertent movement of the shutter member 13 away from the position of closing the recording/reproducing apertures 11, 12.
The shutter locking member 13 is formed by molding synthetic resin and, as shown in FIG. 3, includes an attachment part 14a at a proximal side thereof for attachment to the lower half 7 and a locking arm 14b extending along a curved path from one end of the attachment part 14a. The distal end of the locking arm 14b is formed with an engaging notch 14c engaged by the engaging part 13e of the shutter member 13. The connection portion of the locking arm 14b to the proximal attachment part 14a is a resilient flexible section of a reduced thickness 14d.
The shutter locking member 14 is mounted on the lower half 7 with a pair of attachment pins 7a, 7b of the lower half 7 engaged in through-holes 14e, 14e formed ion the attachment part 14a and with the engaging notch 14c facing the front side of the cartridge main body 9, as shown in FIG. 3.
When the shutter member 13 mounted on the cartridge main body 4 is slid to a position closing the recording/reproducing apertures 11, 12, as shown in FIG. 4, the mating engaging part 13e is engaged in the engaging notch 14c of the shutter locking member 14, which is thereby locked in the position of closing the recording/reproducing apertures 11, 12.
When the above-described disc cartridge which is provided with the shutter locking member 14 for locking the shutter locking member 13 at the position of closing the recording/reproducing apertures 11 and 12, is introduced into a cartridge loading unit of the recording/reproducing apparatus, with the direction shown by arrow A in FIG. 4 as an inserting direction, a shutter actuating pin 16 provided in the recording/reproducing apparatus is intruded into an inlet groove 15 formed on the front side of the cartridge main body 9. As the disc cartridge is introduced into the disc loading unit, the shutter actuating pin 16 rides on the locking arm 14b of the shutter locking member 14, from the outer lateral side of the proximal end towards the distal end thereof, for resiliently flexing the flexible section 14d and thrusting the locking arm 14b into the inside of the cartridge main body 9, as shown by arrow B in FIG. 6. As a result of the movement of the locking arm 14b into the inside of the cartridge main body 9, the mating engaging part 13e ceases to be engaged in the engaging notch 14c, so that the shutter member 13 is moved by the shutter actuating pin 16 in the direction of opening the recording/reproducing apertures 11 and 12.
As best seen in FIGS. 7 and 8, the cartridge main body 9 of the disc cartridge is formed by an upper half 8 and a lower half 7 abutted and connected to each other and is provided with annular supporting ribs 8a, 7b on the inner sides of the upper half 8 and the lower half 7 for supporting a non-recording region N of the magneto-optical disc 1 about the rim of the center hole 3 of the magneto-optical disc 1. By providing these annular supporting ribs 7b, 8a on the cartridge main body 9, the magneto-optical disc 1 is housed within the cartridge main body 9 so that signal recording region extending from the rim of the outer rim of the non-recording region N to the vicinity of the outer rim of the disc 1 is out of contact with the inner surface of the cartridge main body 1. In this manner, the magneto-optical disc 1 may be rotatably accommodated in the cartridge main body 9 so that the signal recording region S is not injured with e,g, grazing.
Meanwhile, if the supporting projections 5b for the metallic plate 5 are formed by thermally deforming several rim portions of the recess 5 as shown in FIGS. 1 and 2, there is a risk that a pointed protuberance 2c can be formed on the one major surface 2a of the disc substrate 2, as shown in FIG. 2.
If the disc having such pointed projection on the major surface of the disc substrate is accommodated in the cartridge main body, there is a risk that the protuberance may contact with the inner surface of the cartridge main body to produce debris removed from the protuberance, such debris being then deposited on the write/read surface of the magneto-optical disc to render it impossible to write and/or read information signals.
Above all, the disc cartridge housing a small-sized magneto-optical disc is of small plan size and thickness, so that the disc housing section in the cartridge main body is also of a thickness only slightly larger than the thickness of the magneto-optical disc. If the above-described protuberance is formed on the disc substrate, it is not possible to prevent the protuberance and the inner surface of the cartridge main body from contacting each other, so that the debris is inevitably produced.
Another problem is that since the supporting rib 8a formed on the upper half 8 supporting the magneto-optical disc 1 is formed as a ring and hence supports only the non-recording region N of the magneto-optical disc 1, a space A is generated between the metallic plate 4 disposed on the radially inner side of the supporting rib 8a and the inner surface of the supporting rib 8a when the magneto-optical disc 1 is thrust upwards towards the upper half 8, as shown in FIG. 8. The result is that, if the metallic plate 4 is thrust by means of the centering hole 3 communicating with the inlet opening 10 and is subjected to a pressure lifting it in the direction shown by arrow y in FIG. 8, only the magneto-optical disc 1 is abutted and thrust by the supporting rib 8a so that the metallic plate 4 may be detached from the disc 1.
If the metallic plate 4 becomes detached in this manner, the magneto-optical disc 1 cannot be attracted and clamped by the magnet provided on the disc table, so that the magneto-optical disc 1 cannot be rotated and hence information signals can not be recorded or reproduced.
The disc cartridge shown herein is of a rectangular shape of as small a size as possible, in association with the size of the disc to be housed therein, for ease of handling and for reducing the size of the recording and/or reproducing apparatus.
With such a disc cartridge, the portion of the disc cartridge provided with the recording/reproducing apertures is lowered in rigidity so that it becomes impossible to assure sufficient rigidity of the cartridge main body, and cartridge main body tends to be flexed and deformed under a smaller external force.
Furthermore, because a groove engaged by a retainer for the shutter member attached to the cartridge main body is formed on the lateral side of the cartridge main body provided with the recording/reproducing apertures and extends along the direction of movement of the shutter member, this portion of the cartridge main body is lowered significantly in rigidity, so that sufficient strength can not be assured. Besides, the shutter member attached to the disc cartridge tends to be detached.
On the other hand, with a disc cartridge in which a groove for permitting entrance of a shutter actuating member for opening the shutter member is formed in the front side of the cartridge main body along which the shutter member is slid, the front side of the cartridge main body which is provided with the groove undergoes significant flexure and deformation because the peripheral wall is removed for forming the groove.
Further, since the shutter locking member of he conventional disc cartridge is formed as a resin molded member, it is extremely difficult to mold the shutter locking member with high accuracy because thermal shrinkage produced at the time of molding.
Besides, in the conventional shutter locking member 13 in which the locking arm 14b is extended by means of the resilient flexible section 14d form one end of the attachment section 14a, it is not possible to assure constant height h from the attachment section 14a as a mounting reference to the cartridge main body 9 to the top of the locking arm section 14b in which the engaging notch 14c is formed. The result is that, when the shutter locking member 13 is attached to the cartridge main body 9 with the attachment section 14a as the mounting reference, it is not possible to assure a constant position of the locking arm 14b facing the groove 15 for the shutter actuating member formed in the front side of the cartridge main body 9, so that the shutter locking member 13 is subjected to variable deflection under a thrust exerted by the shutter actuating pin 16. Thus a stable unlocking operation of the shutter member 13 can not be assured.
Besides, there is a risk that the mating engaging part 13e can not be engaged positively in the engaging notch 14c so that the shutter member 13 can not be positively locked at the position of closing the recording/reproducing apertures 11 and 12 so that there is the risk that the apertures can be inadvertently opened to injure the magneto-optical disc 1 housed within the cartridge main body 9.
In view of the above described status of the art, it is a primary object of the present invention to provide a disc cartridge comprised of a cartridge main body and a disc housed therein, which disc includes a disc substrate of synthetic resin formed with a centering hole and a magnetic plate mounted on one of the major surfaces of the disc substrate for closing the centering hole, in which a clearance for evading protruding parts occasionally formed as a result of attachment of the magnetic plate to the disc substrate is provided on the inner surface of the cartridge main body.
It is a second object of the present invention to provide a disc cartridge in which the magnetic plate can be prevented from being detached from the magneto-optical disc even if an inadvertent force to applied to the magnetic plate.
It is a third object of the present invention to provide a disc cartridge in which the cartridge main body can be prevented from being lowered in rigidity as a result of providing the recording/reproducing apertures for allowing the signal recording region of the disc to be exposed to the outside across the inner and outer disc peripheries for assuring sufficient strength, and in which the disc cartridge can be prevented from being flexed or deformed under a small external force, thereby assuring positive protection of the disc.
It is a fourth object of the present invention to provide a shutter locking mechanism of a disc cartridge in which, even when the shutter member is formed of synthetic resin, the shutter member can be positively locked at a position of closing the apertures provided in the cartridge main body for assuring positive protection of the disc accommodated in the disc cartridge.